. >> schieffer: good evening, scott's off tonight, i'm bob schieffer. well, it is hot all right, and you know that. but here's how hot. if tomorrow lives up to predictions, we'll experience the hottest two-day stretch since 1950. half the population of the united states was under a heat advisory today. oklahoma city recorded its 29th day of 100 degree plus weather. nationwide, at least 22 people are dead. in iowa, 100 head of cattle died in their tracks. a local fire department hosed down the rest of the herd and saved them. we start with dean reynolds in chicago, where it was more than the heat. it was also the pollution. dean? >> reporter: bob, a consequence of this hot weather can be found at one chicago hospital emergency room, where visits are suddenly up 20%, and where doctors say it's because of the heat. the nation's weather today is worse than hot, it's potentially lethal. with 30 states and the district of columbia under heat advisories, watches or warnings, the death toll is expected to rise. meteorologist mike augustyniac explains. >> heat w